Heterogeneity of blood flow and metabolism during exercise in patients with chronic obstructive pulmonary disease.

The study investigated whether the capacity to regulate muscle blood flow (Q) relative to metabolic demand (VO) is impaired in COPD. Using six NIRS optodes over the upper, middle and lower vastus lateralis in 6 patients, (FEV:46±12%predicted) we recorded from each: a) Q by indocyanine green dye injection, b) VO/Q ratios based on fractional tissue O saturation and c) VO as their product, during constant-load exercise (at 20%, 50% and 80% of peak capacity) in normoxia and hyperoxia (FO:1.0). At 50 and 80%, relative dispersion (RD) for Q, but not for VO, was greater in normoxia (0.67±0.07 and 0.79±0.08, respectively) compared to hyperoxia (0.57±0.12 and 0.72±0.07, respectively). In both conditions, RD for VO and Q significantly increased throughout exercise; however, RD of VO/Q ratio was minimal (normoxia: 0.12-0.08 vs hyperoxia: 0.13-0.09). Muscle Q and VO appear closely matched in COPD patients, indicating a minimal impact of heterogeneity on muscle oxygen availability at submaximal levels of exercise.